1. Field of the Invention
The present invention relates to a light power control method for an optical scanning apparatus used on an image forming apparatus.
2. Description of the Related Art
In maintaining image quality on an image forming apparatus of an electrophotographic type, it is important to accurately control light power of an optical scanning apparatus which outputs a laser beam used to form a latent image. Generally, light power control involves controlling a relationship between drive current delivered to a light source and light power of a light beam emitted from a light source.
Generally, on an optical scanning apparatus, an FFP (far-field pattern) and optical axis fluctuate due to differences in image height and light power. To deal with this, Japanese Patent Laid-Open No. 2005-262485 discloses a technique which segments each scanning line into multiple correction sections and determines correction data for each correction section. Furthermore, Japanese Patent Laid-Open No. 2005-262485 proposes to calculate, by interpolation, correction data applicable to an image of any image height and control light power using the calculated correction data.
The invention described in Japanese Patent Laid-Open No. 2005-262485 is very good at maintaining image quality by correcting unevenness of optical characteristics dependent on laser and an optical system. However, there is no fixed relationship among correction data for the different levels of a light power, and the technique must calculate correction data for the different levels of light power separately. Consequently, the invention described in Japanese Patent Laid-Open No. 2005-262485 may require extended computation time.
Furthermore, when updating the correction data, the technique involves transferring items of correction data equal in number to the total number of correction blocks in one scanning line multiplied by the number of beams in semiconductor laser. This tends to extend transfer time. Attempts to shorten the transfer time will involve the need for circuits capable of high-speed transfer, which may result in increased circuit scales.